1. Field of the Invention
This invention relates to ventilation systems, and more particularly to systems in which a plurality of air diffusers are distributed along a duct which encloses a dynamic flow of air.
2. Description of the Prior Art
Suspended ceiling installations have been provided with air ducts which run across the ceiling. Air diffusers which vent air from the duct into the room below are distributed along the length of the duct, typically at spaced intervals. Either heating or cooling air is blown through the duct, thereby creating a dynamic plenum. Upstanding extractor vanes on each of the diffusers deflect a portion of the flowing air out of the duct and into the room. Such a suspended ceiling air distribution system is shown in my U.S. Pat. No. 3,577,904. An improvement on this system is described in my U.S. Pat. No. 3,601,033, in which the diffusers include vents along their sides to permit a return flow of air from the room into the ceiling external to the duct, and a blank-off ember which can be positioned to block the flow of air through the diffuser from the duct into the room. A certain degree of control over the distribution of treated air from the duct is thus attainable by a selective positioning of the blank-off members over particular diffusers.
While my U.S. Pat. No. 3,601,033 offers an improvement in the distribution of treated air, it is not optimal. The described air ducts may be characterized as enclosing dynamic plenums, i.e., plenums having a directional flow of air. Since the ducts are of finite length and are generally closed or restricted at the downstream end, a static pressure progressively builds up as the downstream end is approached. This static pressure causes the volumetric rate of air flow through the downstream diffusers to exceed the rate at which air is vented from the upstream diffusers, thus violating the situation in which air is ideal, vented through all the diffusers at the same rate. The resulting flow rate discrepancies can result in an uneven temperature distribution in the vented area. Aside from the discomfort of being in an area that is either too hot or too cold, the occupants of the building may take corrective action by blanking off one or more diffusers if a system such as that described in my U.S. Pat. No. 3,601,033 is used. Such action could further gravate the situation in areas where the diffusers have not been blanked off. The result is discomfort to the occupant, and an inefficient use of the energy expended to heat or cool the air flowing through the duct.
The construction of partitions or walls between the diffusers of a continuous duct is another situation in which the uneven venting of air in the prior art is a problem. Again, persons in rooms which receive either too much or too little treated air may become uncomfortable, and may blank off their individual diffusers and thereby worsen the problem in other rooms.